Principal Investigator / Program Director (Last, first, middle) [unreadable] Ziskin, MarvinC. Project 1: Fundamental Physical Interactions of Millimeter Waves with the Skin ABSTRACT Millimeter waves (MW) have been shown to produce biological effects and are being used for medical treatment. Due to shallow penetration, MW interact primarily with the skin structures. It was accepted that exposures at intensities of 10 mW/cm2 and higher were able to produce thermal effects on biological substances due to temperature elevation and a high heating rate. The latter factor could play an important role in stimulating nerve endings in the skin. Recent theoretical analyses showed that due to thermal noise, the direct interaction of MW on molecular and cellular levels at exposure intensities less than 10 mW/cm2 could not affect biological systems. Hence, to identify the mechanisms of biological effects of MW, it is very important to characterize quantitatively the power density and absorption at different points within the skin, and the temperature elevations and heating rates in the locations of thermosensitive structures of the skin. As the wavelength of MW is comparable with the thicknesses of skin layers, the frequency-dependent absorption of MW differs for layers. Non-homogeneous structures of the skin such as blood vessels and sweat ducts can disturb the power density in nearby areas. Thus, the present studies are designed to determine the frequency dependence of the MW energy deposition within different layers and non-homogenous appendages of the skin. Using multilayer tissue models, we will investigate theoretically and experimentally the MW heating of the skin under different exposure conditions and effect of blood flow and water evaporation on the temperature elevation. We will also examine the capability of MW to elicit local vasodilatation in the skin. Some dosimetry methods such as specific absorption rate measurements, which were widely used for quantifying the absorption energy through entire radiofrequency spectrum, are not appropriate for shallow penetrating MW, and they should be modified when applied to MW frequencies. The new methods developed in our study for determination of MW energy deposition and heating of the skin will be used for establishing adequate dosimetry. The results of the proposed project will be utilized in evaluation of the biophysical mechanisms of the MW interaction with skin structures, and for improving dosimetry in the animal studies of the other projects of the Center.